The present invention relates to the field of static electricity detectors and, in particular, to detectors which sense the presence of charged objects in a large area.
In certain manufacturing concerns, static electricity is a very major problem. A small amount of static charge can destroy certain semiconductor devices and wreak havoc during photographic processing. Static electricity is often carried on workers' clothing into a work area and transferred into a work area. In fact, anyone in or near a work area can inadvertently damage an electricity-sensitive process with static charge.
Because the effects of static charges are usually not immediately known, a semiconductor device destroyed by static charge may not be detected until it is later tested or used. By the same token, even when an inoperable device is found, the cause of the failure cannot always be determined. This uncertainty makes it difficult to improve manufacturing and processing techniques.
Workers in industries where static electricity is a problem are usually "grounded" through wires running from a point at ground potential to conductive bracelets on the workers' wrists. This type of protection is limited because a broken or loose ground wire destroys the ground path. Grounding bracelets also do not prevent damage caused by non-workers who enter a charge-sensitive work area without taking proper grounding procedures.
Electric field meters are also used in industries where static electricity is a problem. These meters are directed at a work area to register the amount of charge moving into and out of that area. Unfortunately, the range of such meters is limited, so many are usually required to cover a work area. Furthermore, the meters give no indication of how great a charge has been transferred into the area nor how far away the charge was from the meters. An electric field meter will register the same intensity for a small charge close to the meter and for a larger charge farther away from the meter.
It is, therefore, an object of the present invention to detect the movement of harmful electric charges into a work area.
It is also an object of the present invention to detect the movement of such charges into a work area with a single device, even though the work area is large.
It is a further object of the present invention to detect the movement of charge into an area such that it can later be determined which devices and processes have been affected.
Additional objects and advantages of the present invention will be set forth in part in the description which follows and in part will be obvious from that description or may be learned by practice of the invention. The objects and advantages of invention may be realized and obtained by the methods and apparatus particularly pointed out in the appended claims.